1. Technical Field of the Invention
This invention relates to radio telecommunication systems and, more particularly, to a system and method of completing calls to busy mobile subscribers in a radio telecommunications network.
2. Description of Related Art
With the widespread growth of radio telecommunications services, mobile subscribers demand increased capabilities found in land-based Public Switched Telephone Network (PSTN) systems. One such service offered in PSTN based systems is automatic callback which enables a calling party to connect with a busy called party, once the called party can accept calls (i.e., when the called party finishes his first call).
However, there are obstacles preventing the optimal use of this automatic callback service for subscribers in a radio telecommunications network. First, difficulties arise in locating a mobile station (MS), since the MS can travel a considerable distance between calls. Second, in order to efficiently provide an automatic callback service for mobile subscribers, the impact upon the entire radio telecommunications network must be minimized. Adding a service for a relatively small number of MSs which requires extensive changes to the entire radio telecommunications network, is not cost effective for system operators. Therefore, the callback service must not require drastic change across the entire radio telecommunications network. In addition, the use of call connections, known as trunks, should also be minimized during the automatic callback process since these are valuable system resources. The service becomes expensive if too many resources are required to implement this service. Therefore, the implementation and actual use of the automatic callback service in radio telecommunications networks must be capable of locating the MS, while efficiently utilizing network resources.
Although there are no known prior art teachings of a solution to the aforementioned deficiency and shortcoming such as that disclosed herein, prior art references that discusses subject matter that bears some relation to matters discussed herein are U.S. Pat. No. 5,406,616 to Bjorndahl (Bjorndahl) and U.S. Pat. No. 5,287,551 to Gustafson, Jr. et al. (Gustafson).
Bjorndahl discloses a method of effecting automatic callback in a mobile telecommunications system. A centrally located home location register (HLR) keeps an account of where all mobile stations registered in the mobile telecommunications network are located, with the aid of local databases called visitor location registers (VLRs). A gateway mobile switching center (G-MSC) provides switching functions to mobile stations within its operating area and an interface between the PSTN and the Public Land Mobile Network (PLY). Upon a mobile station exiting the service area of its home MSC, a visiting mobile switching center (V-MSC) provides control and switching functions for the mobile station within a defined service area controlled by the V-MSC.
The calling party (who may be located within the PSTN or the PLMN) calls the called mobile subscriber, which causes a trunk to be seized from the G-MSC to the V-MSC, and finds that the subscriber is busy. The calling party then dials a code which results in a reference being stored in a queue in the HLR. When the called mobile subscriber is free to receive a call, the calling party is informed of the idle status of the mobile station by an announcement machine typically found in mobile switching centers. The calling party then lifts his telephone receiver and a connection is completed between the two subscribers. While waiting for the called subscriber to become available, the trunk from the G-MSC to the V-MSC remains tied up.
There are several disadvantages to the Bjorndahl method. First, the continued utilization of the trunk during the entire automatic callback process wastes this valuable network resource. Additionally, all mobile switching centers which might interact with the MS must be modified for the automatic callback service to keep the trunk established even though the MS is not currently available. Thus, Bjorndahl does not teach or suggest a system or method of effecting an automatic callback while minimizing the utilization of network resources and reducing the required modifications to the existing radio telecommunications network.
Gustafson discloses an apparatus and method for issuing busy callbacks on a voice channel to busied communication units on a trunked radio communication system. A control resource issues a busy signal to a communication unit when a requested communication unit is unavailable. The radio communication unit receiving the busy signal may still participate in a second communication while in a busied state. The resource controller is capable of allowing the busied communication unit to participate in a second communication unit on a second communication resource and issuing the call-back signal during the second communication. However, Gustafson requires that at least one trunk be maintained during call-back from the busy communication unit. Additionally, significant modifications are necessary to implement this busy call back system into current radio telecommunication networks. Thus, Gustafson does not teach or suggest a system or method of effecting an automatic callback while minimizing the utilization of network resources and reducing the required modifications to the existing radio telecommunications network.
Thus, it would be a distinct advantage to have a system and method for effecting automatic callback which minimizes the resources of the radio telecommunications network while reducing any required modifications to the existing radio telecommunications.